The field of this invention is that of tools used for the cleaning of pipelines, especially the long extended reach pipelines in offshore areas. As hot production crude is produced from the reservoirs below the ocean floor up to the wellhead equipment at the ocean floor and then thru pipelines along the ocean floor, it is cooled by the relatively cool temperature of the ocean water. In deepwater, the temperature can be as cold as 35 degrees Fahrenheit.
A characteristic common to a majority of the oil produced is that there is a wax component to the oil which will deposit on the walls of the pipeline and become a solid at temperatures well above the 35 degrees Fahrenheit. In fact, some of the waxes become a solid at temperatures above 100 degrees Fahrenheit, and so can be deposited or plated on the internal diameters of the pipelines at any expected ambient temperature. The process is similar to discussions of blocking of the arteries of a human being, with a thicker coating building up with time. Some pipelines have become so plugged that more than 90% of the flow area is blocked with the waxes, or are simply plugged.
Typically, as the wall becomes layered with wax as the temperature of the oil goes below the solidification temperature of the particular waxes in the produced fluids. The waxes act as a sort of insulation to the flow in the pipeline, allowing it to maintain a higher temperature for a greater distance. The effect of this is to extend the distance along the pipeline to which the wax is plating onto the internal diameter of the pipeline.
A common cure for the wax plating out on the internal diameter of the pipeline is to insert a pig into the flow stream and let the pig remove some of the wax. A pig is typically a cylindrical or spherical tool which will brush against the internal diameter of the pipeline in hopes of removing the deposited waxes. In pipelines with a high incidence of deposited waxes, a regular maintenance of pigs is normally prescribed as a preventative to pipeline blockage.
One problem with the pigs is that the deposited waxes are relatively soft and contain a lot of oil. To some extent, the pigs actually compress the waxes against the wall and squeeze the oil out, leaving a harder and stronger wax remaining.
A second problem is that when the wax layer on the internal diameter of the pipe is too thick, sloughing off may occur. If the wax starts to separate from the wall and continues, the pig begins to literally plow a block of wax ahead of itself. This will continue driving more and more wax off the wall of the pipeline until the pressure of the pipeline will no longer be able to move the mass. At that time you have a full pipeline blockage, which cannot be moved by pressure from either end.
If you imagine that you have an 8″ internal diameter pipeline which is plugged for 1000 feet, the volume of the plug would be over 2600 gallons of wax. Depending on the particular wax and cleaning chemicals, it would probably take 10 gallons of chemicals to remediate one gallon of wax, so that would be 26,000 gallons of expensive chemicals to buy. If the wax was 5 miles from the point of entry into the pipeline, it would take almost 70,000 gallons of chemicals in the pipeline just to get to the wax blockage to remediate it.
It is easy to understand the benefits of a system which would clean wax blockages mechanically, eliminating the need for the expensive chemicals.